Although ignore lists are useful, they can also be the spawn of satan too. As Forrest Gump allegedly said:
"Forum posts are a liiiiike a box of cho-co-lates. You never knoooow when a troll will make a good one..."
My advice is create your own ignore function, unless you *really* feel a poster will never make a good contribution. If you see a poster you think is a troll, scan the post quickly and see what you think. At the end of the day, if they were on your ignore list you'd have seen none of the post anyway. Likewise, if that same person comes up with a quality post or idea out of the blue, you'll miss it without any kind of notification, and that could be your loss.
Ignore List = Easy and Clumsy way of missing quality posts, and generalising that someone will never make a post worth reading, which is something you cannot predict (sorry I'm a programmer)
EDIT: Flaming I don't like, and it's a shame it happens (I have been guilty in the past, I'll admit). Offtopic wandering is a completely different thing - it happens, it's a fact of forum life, and it aint gonna change (yes I'm guilty of this too, even more so

) People should not find themselves on ignore lists for posting offtopic replies